Bump pywatchman from 1.4.1 to 2.0.0 in /requirements (#2169)

Bumps [pywatchman](https://github.com/facebook/watchman) from 1.4.1 to 2.0.0.
- [Release notes](https://github.com/facebook/watchman/releases)
- [Commits](https://github.com/facebook/watchman/commits/v2.0)

---
updated-dependencies:
- dependency-name: pywatchman
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

requirements/django-server-requirements.txt

@@ -1,2 +1,2 @@
 # to allow Watchman to be used with Django Development Server
-pywatchman==1.4.1
+pywatchman==2.0.0